Marcus Sedgwick 
Dark Peak [PDF ebook] 

During a long, hot summer, two children, Stephanie and Stephen, go missing while on a school trip to Lud’s Church, a deep chasm in the heart of the Peak District. Porter and his friend, Sam, are sent to fetch help. When they return they are surprised to find that although Stephanie has been found, no one is even looking for Stephen anymore. Why can no one remember what’s happened him? What happened in the dark of Lud’s Church? And why does Porter get the feeling that supernatural forces from deep in the past are at play? Marcus Sedgwick fuses mythology and mystery to create a compelling tale that is perfect for less-confident readers.